The eye movements of people with neurological disease differ significantly from those of healthy people. In addition, eye movements among people with seemingly similar but different neurological diseases can also be different from each other. Because of the importance of accurate diagnosis of neurological diseases, a need exists for better methods of evaluating such differences.
The eyes do not stay perfectly still during visual fixation. Fixational eye movements and saccadic intrusions continuously change the position of the gaze.
Microsaccades are rapid, small-magnitude involuntary saccades that occur several times each second during fixation; microsaccades counteract visual fading and generate strong neural transients in the early visual system. Microsaccades may also drive perceptual flips in binocular rivalry. Microsaccade rates and directions are moreover modulated by attention, and thus generate rich spatio-temporal dynamics. Further, fixational eye movements as a whole enhance fine spatial acuity.
The most common type of saccadic intrusion is referred to as a square wave jerk (SWJ). SWJs are characterized by one small horizontal saccadic movement that moves the eye away from the fixation target, followed by a corrective saccade towards the target shortly thereafter. SWJs are prevalent in some neurological diseases such as progressive supranuclear palsy (PSP). However, they are also common in normal healthy subjects and in patients with Parkinson's disease (PD).
Patients with PSP and those with early stages of PD often appear to present similarly. It would be beneficial to be able to differentially diagnose one disease from the other in a non-invasive manner. The following disclosure provides one such differential diagnostic method.